This invention a and relative device to control the force applied to the electrode-bearing arms of an electric arc furnace.
To be more exact, the invention concerns a method and device suitable to control constantly the force applied to the electrode-bearing arms of an electric arc furnace, the force being suitable to lift and position the electrode in a required manner in a vertical direction.
By means of the invention it is possible also to monitor the mass of the electrode at any time during smelting so as to know the relative wear of the electrode and to be able to act accordingly.
Document DE 2.312.603 is known and concerns a device to prevent breakage of electrodes in electric furnaces having electrical, electrohydraulic or electropneumatic regulation, in particular for smelting of scrap; this device consists of an operational cylinder actuated by a fluid under pressure so as to lift and lower the electrodes, the control means of the cylinder being adjustable by means of an electrical commutator device which responds in the event of excursions of the current of the electrodes from the nominal value.
In the above document a pressure switch is connected to the circuit under pressure of the operational cylinder and transmits by means of its switch to the control means a signal to lift the electrodes in the event of a drop of pressure in the operational cylinder when the electrodes contact non-conductive materials and when a given response pressure is reached in the operational cylinder.
The circuit is also connected to a switch which, upon reduction of pressure in the operational cylinder, interrupts simultaneously the current fed to the electrical regulation circuit and, upon attainment of the response pressure, restarts the current, which in turn transmits a signal for lowering of the electrodes.
However, the contents of the above document involve a plurality of unsuitable indications. The circuit cannot monitor constantly and continuously by means of the pressure switch the variable value of the static pressure in the cylinder and therefore can perform neither an automatic control of the value of wear of the electrodes nor the memorisation of the value of the weight of the arm at every speedy descent of the electrodes for the beginning of smelting, nor regulation in a closed circuit with a servovalve having a speedy response for control of the electrodes by means of a pressure control; the circuit is not even able to carry out automatic regulation with an electronic system to regulate the electrodes so as to prevent any short circuits at the electic arc during smelting, nor can it prevent automatically an accidental breakage of the electrodes.
The above known document discloses operation by means of a timer and a relay and therefore provides for regulation in steps, which in itself is unstable, slow and discontinuous.
Moreover, the known document employs a pressure switch, which of necessity has to be set with a given minus step as compared to the minimum actual value; and therefore when the pressure switch senses the pressure of actuation, there is the danger that the electrode may be already broken since this step of interval may be too great for the typical requirements of the electrode.
Furthermore, the above known document does not disclose acting by perforating mechanically any insulating material found between the electrode and the metallic mass to be melted.